1. Field of the Invention
This invention relates to a method for refining a sugar liquor containing impurities including colloidal or suspended materials, colorants, ashes, microorganisms and odor emitting substances. It also relates to a method for refining a sugar liquor through decoloration and desalting and, more particularly, to a method for refining sugar liquor using ion exchange resins.
2. Prior Art
The major portion of the impurities contained in the raw sugar is included in a molasses film affixed to the crystal surface and is mainly composed of coloring matter, ashes, invert sugar, fatty acid, amino acids, colloidal matter and microorganisms. The conventional practice has been to remove these impurities to some extent by a washing operation to separate the raw sugar into a so-called washed sugar and washed molasses before proceeding to the subsequent refining process.
Meanwhile, about 10% of sucrose based on raw sugar is disolved in the washed molasses, it being extremely difficult to recover sucrose from these washed molasses. This sucrose recovered after crystallization from the washed molasses is low in commercial value and must be subjected to redissolution thus resulting in lowered refining yield. Moreover, the complicated process represents a major factor in lowering the process capacity.
Attempts have been made in this nation to dissolve and refine raw sugar without an intermediate sugar washing process, as exemplified in the Japanese Patent Publication Nos. 24494/1965 and 19595/1968. However, none of them have won commercial success.
The reason for such failure is presumably ascribable to the fact that no pre-treating refining method of reducing the load of the ion exchange resin process has been evolved. Therefore, when the refining of the unwashed sugar liquor is tentatively performed through improvement of the ion exchange resin arrangement or the manner of passing or regenerating the sugar liquor, the capacity of the ion exchange resin is drastically lowered with increase in the number of cycles, resulting in failure in producing desired decoloration and desalting effects or ultimate economic effects.
A large amount of suspended materials are contained in sugar liquor, especially unwashed sugar liquor, so that a pretreating refining method for effectively removing these suspended materials is strongly desired. Should these suspended materials be removed effectively, the load of the ion exchange resin process may be lowered, so that one may expect more effective decoloration and desalting.
It is however extremely difficult to remove the suspended materials contained in the unwashed high concentration sugar liquor, washed molasses or a variety of molasses by a filtration or a centrifugation method. Although these may be removed by special filtration operations, such as ultra precision filtration, self-extrusion film or ultrafiltration film methods, the operating costs are unbearably increased.
On the other hand, application of ion exchange resins to the sugar refining industry has been made extensively, such that it is not too much to say that this system is adopted by almost all sugar makers in some form or other.
However, this system is mainly intended for decoloration by a unitary tower packed with a chlorine type strong basic anion exchange resin, and is no more than a technique of partially refining the washed sugar liquor. Although the method for refining the unwashed sugar liquor is an ultimate target of sugar refining, the prior art system lacks in the capacity of removing impurities, mainly the decoloration and desalting in the course of the ion exchange resin process, such that the conventional sugar refining process cannot be superseded by the ion exchange resin system not only in quality but economically.
The present inventors have been engrossed in developing a desalting and refining technique through the use of ion exchange resins. It has now emerged from our experiences that evolution of some technical measures for combatting the lowering of the capacity of the strongly basic anion exchange resins is utmost importance.
In this connection, there are proposed various techniques centered about resin regeneration and restoration methods, as exemplified by the Japanese Patent Publications Nos. 11385/1980, 46218/1980 and 24663/1984.
Of these, the method of desalting the washed sugar liquor, known as the so-called improved reverse method, is the currently used refining method by ion exchange resins in which artifices are used for preventing contamination of the strongly basic anion exchange resin. These artifices include arranging a Na type strongly acidic cation exchange resin, a strongly basic anion exchange resin and a weakly acidic cation exchange resin in this order and conducting the regenerated waste liquid or the hydrochloric acid containing saline water from the weakly acidic cation exchange resin through the strongly basic ion exchange resin for preregeneration.
Although excellent in preventing contamination of the strongly basic anion exchange resin, this system has a drawback that it is of the load type or Cl type since the resin which ought to be used inherently in the isolated form is pre-regenerated with the hydrochloric acid containing saline water which is the regenerated waste liquid by the weakly acidic cation exchange resin. That is, this known system has a drawback that the efficiency of final regeneration by sodium hydroxide and the desalting efficiency are lowered. In addition, the ion exchange resin that has lost its desalting capacity has to be passed to the regenerating operation, even though it still has some decoloration capacity, which proves to be an inconvenience from the viewpoint of effective resin utilization.
For obviating this deficiency, an attempt has been made to divide the strongly basic anion exchange resin in two and to pre-regenerate only the former half resin while only finally regenerating the latter half resin. However, with this system, contamination of the latter half resin cannot be eliminated, such that it becomes necessary to obviate the problem of resin contamination every twentieth cycle by the pre-regenerative operation consisting in treating the resin with a hot hydrochloric acid and with a sodium hydroxide containing saline water in this sequence. The result is a complicated procedure and the necessity of using additional pre-regenerative agents.